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University College of Medical Science & GTB Hospital, Delhi

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1 University College of Medical Science & GTB Hospital, Delhi
Cardiac Rhythm and Anaesthesia: Basics of ECG Abnormal rhythms relevant to anaesthetic practice Antidysrhythmic agents Management of perioperative arrhythmias Abnormal rhythms relevant to anaesthetic practice Management of perioperative arrhythmias Antiarrhythmic agents Dr. B. Uma University College of Medical Science & GTB Hospital, Delhi

2 Basics of ECG

3 Objectives What is an ECG ECG indications
Review of the conduction system ECG recording ECG paper ECG leads 5. ECG interpretation

4 What is an ECG? The electrocardiogram (ECG) is a graphic recording of the electrical potentials generated by the heart. The signals are detected by means of metal electrodes attached to the extremities and chest wall and are then amplified and recorded by the electrocardiograph Introduced by William Einthoven in 1901


6 ECG Indications Monitoring Diagnosis
In the perioperative setting, ECG serves 2 main functions – monitoring and diagnosis ECG monitoring is mandatory and standard of care during all kinds of procedures With appropriate lead combinations, most arrhythmias and myocardial ischaemic events can be diagnosed.

7 ECG Indications… Preoperative period Risk Assessment
Assess the baseline cardiac status Information regarding MI, conduction or rhythm abnormalities Reveals findings related to life threatening metabolic disturbances or susceptibility to sudden cardiac death

8 ECG Indications… Intraoperative period
Monitoring to detect changes in rate and rhythm or myocardial ischaemia Monitoring of proper function of pacemakers or implantable cardiac defibrillators in patients undergoing surgery with these devices in place In intraop period, besides detecting changes in rate & rhythm or myocardial ischaemia, it also enables the anaesthesiologist to monitor the proper function ;l

9 ECG Indications… Postoperative period Monitoring
Important in high risk patients when new ischemic or rhythm changes are suspected A postoperative 12 lead ECG is often obtained in high risk .....

10 ECG Paper

11 The Normal Conduction System

12 Talk about PR interval, U wave and J Junction

13 P wave caused by atrial depolarization Right atrial activation reflected by ascending limb of P wave Duration= s Left atrial activation reflected by descending limb of P wave Duration= s Hence, total duration= s (maximum duration=0.11s) Maximum normal amplitude=2.5mm

14 QRS complex is caused by the ventricular depolarization
QRS duration sec QRS amplitude S amplitude in V1 + R amplitude in V6 < 3.5 millivolt (mV) R in V5 or V6 < 2 mV

15 The ST segment and T wave reflect ventricular repolarization
ST segment duration= s T wave duration=0.16 s T wave should be at least ⅛th but less than ⅔rd of the amplitude of the corresponding R wave

16 ECG Leads Leads are electrodes which measure the difference in electrical potential between either: 1. Two different points on the body (bipolar leads) 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart (unipolar leads)

17 ECG Leads The standard ECG has 12 leads: 6 Frontal plane leads
6 Horizontal plane leads Frontal plane leads - oriented in frontal or coronal plane of the body and consist of standard leads I, II, III and augmented limb leads AVR, AVL, AVF. Horizontal plane leads - oriented in transverse or horizontal plane of the body and are formed by precordial leads V1-V6.

18 Standard Limb Leads

19 Standard Limb Leads

20 Augmented Limb Leads

21 All Limb Leads

22 Precordial leads

23 aVR, aVL, aVF (augmented limb leads)
Summary of Leads Limb Leads Precordial Leads Bipolar I, II, III (standard limb leads) - Unipolar aVR, aVL, aVF (augmented limb leads) V1-V6

24 Anatomic Groups (Summary)

25 3 Electrode ECG monitoring
Electrodes placed on the torso to reduce artifacts from limb movement RA/LA electrodes placed in right and left infraclavicular fossae LL leg electrode below the left rib cage Most common mode in OR and ICU Good enough to detect HR and VF Inadequate for detecting complex arrhythmias and ST segment monitoring

26 5- Electrode ECG monitoring

27 Modified Chest leads Modified chest leads (MCL) are useful in detecting bundle branch blocks and premature beats. Lead MCL1 simulates chest lead V1 and views the ventricular septum. Lead MCL6 simulates chest lead V6 and views the lateral wall of the left ventricle CS 5 (RA electrode placed under the right clavicle and LA electrode placed in the V5 position) for detection of anterior myocardial wall ischaemia CB5 (RA electrode over the center of the right scapula and LA electrode in the V5 position) for detection of ischaemia and supraventricular arrhythmias

28 Ten-Electrode, Twelve-Lead ECG Monitoring

29 The Right-Sided 12-Lead ECG
The limb leads are placed as usual but the chest leads are a mirror image of the standard 12-lead chest placement Clinical significance: Patients with an acute inferior MI should have right-sided ECGs to assess for possible right ventricular infarction

30 Invasive Electrocardiographic Monitoring
Esophageal electrocardiogram: Much closer to atria. Hence better option when p waves recording is uncertain Detection of posterior wall ischaemia Esophageal electrodes incorporated into esophageal stethoscopes and welded to conventional electrocardiographic wires

31 : Intracardiac electrocardiogram: Endotracheal electrocardiogram:
Multipurpose pulmonary artery catheter with 3atrial and 2ventricular electrodes for intracavitary ECG Relatively insensitive to electrocautery Endotracheal electrocardiogram: Endotracheal tube with 2 electrodes embedded Diagnosis of atrial arrhythmias in pediatrics Intracoronary electrocardiogram: Coronary guide wire during angioplasty is used Greater detection of acute ischaemia

32 ECG Interpretation Rate Rhythm QRS axis P Wave PR Interval QRS Complex
QT Interval ST Segment

33 Documentation: name of the patient and the date and time it was recorded.
Calibration signal: The amplifier gain is normally adjusted so that a 1 millivolt signal through the ECG amplifier results in a vertical deflection of 10 mm (two large ECG squares). All voltage measurements on the ECG depend entirely on the accuracy of this calibration signal.

34 Determining the Heart Rate
Rule of 1500 Heart rate=1500/no. of small boxes between adjacent RR intervals Rule of 300 Heart rate=300/no. of big boxes between adjacent QRS complexes 6/3 second rule No. of RR intervals in 3sec multiplied by 20 or No. of RR intervals in 6sec multiplied by 10 Check source of rules

35 What is the heart rate? 1500/30 = 50 bpm

36 What is the heart rate? Count number of large boxes between first and second R waves= /7.5 large boxes = rate 40

37 What is the heart rate? Count 30 large boxes, starting from the first R wave. There are 8 R-R intervals within 30 boxes. Multiply 8 x 10 = Rate 80

38 Rhythm Normal: Each QRS preceded by a P wave with a regular PR and RR interval and a rate between 60 and 100 bpm Irregular Regularly Irregular Irregularly Irregular Tell that arrhythmias will be discussed in details in the next part

39 The QRS Axis The QRS axis represents the net overall direction of the heart’s electrical activity Direction of the axis determined on the basis of the hexaxial reference system

40 The QRS Axis By near-consensus, the normal QRS axis is defined as ranging from -30° to +90°. -30° to -90° is referred to as a left axis deviation (LAD) +90° to +180° is referred to as a right axis deviation(RAD) Some books mention normal range upto +100

41 Movement of the electrical impulse towards the positive electrode will result in a positive deflection on the ECG. Movement of the electrical impulse towards the negative electrode will result in a negative deflection on the ECG. Movement of an electrical impulse perpendicular to a line between the positive and negative electrodes results in a biphasic deflection on the ECG.

42 Determining the Axis Predominantly Positive Predominantly Negative

43 The Equiphasic Approach
1. Determine which limb lead contains the most equiphasic QRS complex. The fact that the QRS complex in this lead is equally positive and negative indicates that the net electrical vector (i.e. overall QRS axis) is perpendicular to the axis of this particular lead. 2. Examine the QRS complex in whichever lead lies 90° away from the lead identified in step 1. If the QRS complex in this second lead is predominantly positive, than the axis of this lead is approximately the same as the net QRS axis. If the QRS complex is predominantly negative, than the net QRS axis lies 180° from the axis of this lead.

44 Equiphasic Approach: Example 1
The Alan E. Lindsay ECG Learning Center ; Equiphasic in aVF  Predominantly positive in I  QRS axis ≈ 0°

45 Equiphasic Approach: Example 2
The Alan E. Lindsay ECG Learning Center ; Equiphasic in II  Predominantly negative in aVL  QRS axis ≈ +150°

46 Two lead approach Look for net QRS deflection in leads I and aVF
If both +ve – Normal axis If I +ve & aVF predominantly –ve – Left axis deviation If I –ve & aVF +ve – Right axis deviation

47 Calculation of Axis – Third Approach
Calculate the net QRS deflection in lead I and aVF E.g. in lead I, Q wave measures 3 small squares & R wave measures 6 small squares - net deflection is +3 Similarly, net deflection in aVF is -5 Cardiac vector is thus sum of individual vectors from leads I and aVF

48 P Wave Best evaluated in standard lead II and lead V1
In standard lead II P wave is pyramidal with a rounded apex In lead V1 biphasic P wave with an initial positive and a terminal negative deflection Axis within 40°to 60°

49 P Wave – Clinical Significance
P Pulmonale -Tall peaked P wave -Amplitude in lead II >2.5 mm -Duration WNL -Expression of right atrial enlargement P Mitrale -Double peaked, notched or camel humped P wave -Negative deflection in V1> 1mm -Duration of notch > 0.04s -Expression of left atrial enlargement

50 PR Interval PR interval - between beginning of P wave and beginning of QRS complex Duration = 0.12 to 0.20 sec Reflects time taken for conduction of impulse from SA node to the ventricles through the AV node Long PR interval: first degree heart block, hyperkalemia Short PR interval: WPW syndrome

51 QRS Complex - Interpretation
QRS interval QRS voltages Precordial R-wave progression Abnormal Q waves

52 The QRS Complex

53 QRS Complex – Clinical Significance
LVH RVH Ventricular ectopics RBBB LBBB Hemiblocks Add ECGs to show LVH and RVH, say that rest will be discussed later

54 RVH

55 LVH

56 Q waves Pathologic Q waves are a sign of previous myocardial infarction. The precise criteria for pathologic Q waves: Q-wave 0.04 s in duration Deeper than one fourth of the following R wave in voltage Q wave is deep usually greater than 4mm in depth

57 ST Segment Represents greater part of ventricular repolarization
Merges smoothly and imperceptibly with the proximal limb of T wave Leaves the baseline immediately after its origin; hence not isoelectric Flat, downsloping, depressed: coronary ischaemia, hypokalemia, digitalis toxicity Elevation: MI Check normal variant

58 T Wave Represents the repolarization of the ventricles
Last half represents relative refractory period Positive deflection in most leads Negative deflection in AVR Biphasic in V1 T wave inversion: coronary ischaemia Tall tented T wave: hyperkalemia Flat T wave: hypokalemia Heavily notched: pericarditis

59 ST-T segment: Significance
ST-T segment is the component of ECG most sensitive to acute myocardial ischaemia Transmural ischaemia→ ST elevation accompanied by tall positive (hyperacute) T waves Subendocardial ischaemia→ ST depression Myocardial infarction→ pathologic Q waves

60 QT Interval Interval from the beginning of the QRS complex to the end of T wave Represents the total duration of ventricular electrical activity Corrected QT interval (Q-Tc)= QT/√R-R Normal values= 0.39±0.04 s.

61 QT Interval –Clinical Significance
Prolonged QTc interval: Acute myocarditis Acute MI Torsades de pointes Romano Ward syndrome Shortened QTc interval: Digitalis effect

62 U Wave Small rounded deflection (< 1 mm) that occurs immediately after T wave and has same polarity as T wave Best seen in leads V2-V4 ?repolarization of papillary muscles or purkinje fibres Prominent U wave: hypokalemia, drugs e.g. dofetilide, amiodarone, sotalol, quinidine, procainamide, disopyramide Inverted U wave: Sign of ischaemia

63 J Point The J point in the ECG is the point where the QRS complex joins the ST segment. It represents the approximate end of depolarization and the beginning of repolarization as determined by the surface ECG. There is an overlap of 10 milliseconds.

64 Some Practical Points Skin prepared by-
Hair should be shaved Skin cleaned with spirit Abrade skin lightly Muscle tremor presents as artifact. Electrode should be placed over bony prominence. Electrodes – pregelled, disposable Broken electrodes to be discarded

65 Artifacts Equipments interfering with ECG: 60 hz power lines
Electrocautery (mc) Cardiopulmonary equipment Defibrillators Transplanted heart(pseudoartifact)

66 What is the axis?




70 Outline Factors causing perioperative arrhythmias
Mechanisms of arrhythmogenesis Sinus Rhythms Atrial Rhythm disturbances Junctional Rhythms Ventricular Rhythm disturbances Conduction blocks

71 Arrhythmias Abnormality of cardiac rate, rhythm or conduction
Most frequent perioperative cardiac abnormality Both during cardiac and non cardiac surgeries With general and regional anaesthesia

72 Factors contributing to perioperative arrhythmias
Patient related Anaesthesia related Surgery related

73 Patient related factors
Pre existing cardiac disease – higher incidence, more fatal CNS stimulation – SAH → ST-T changes Old age – Post-op AF frequent due to degenerative changes in atrial anatomy

74 Anaesthesia related factors
Endotracheal intubation General anaesthetics Halothane (reentry, sensitization to catecholamines), enflurane, sevoflurane (severe bradycardia), desflurane (QTc prolongation) Drugs blocking reuptake of catecholamines- ketamine Local anaesthetics Inadvertent intravenous injection of large dose - cardiac arrest High thoracic levels of regional anaesthesia- bradyarrhythmias Abnormal arterial blood gas and electrolyte levels Hypercarbia, hypoxia, hypocarbia a/w hypokalemia

75 Surgery related factors
Autonomic reflexes Peritoneal traction, pressure on vagus - sinus bradycardia, AV block, asystole Oculocardiac reflex- bradycardia, asystole IJV cannulation Cardiac surgery Release of aortic cross clamp Placement of venous cannulae Retraction of the heart Suturing over the atrium

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